The cooling of gaseous fluids containing humidity and, in particular, the cooling of humid air, is required in many circumstances. Cooling of ambient atmosphere is required in buildings, domestic dwellings, and in appliances such as refrigerators, and in storage rooms and the like. It is also, of course, required in vehicles such as automobiles and many delivery vehicles and trucks, and in aircraft and marine craft.
Many different proposals have been made for cooling gases and, in particular, for the cooling of air. The most popular system in widespread use is the use of the compression and expansion of a heat exchange medium in the form of a gas which can be compressed into a liquid state, and then is allowed to expand into a vapour state once more, the so-called compression/expansion cycle. In most cases, the gas used is known under the trade mark "Freon". These systems using the compression/expansion cycle require a relatively large input of power for the compression cycle. This is usually provided by a pump, and an electrical motor or other prime mover. For example, in the case of an automobile, a power takeoff is simply connected directly to the automobile engine usually by means of a belt.
In most other cases, electrical motors are used as is well known. These systems require more and more power, as the cooling load is increased. Thus, in extremely hot seasons of the year, very large amounts of electrical power are required simply to maintain a stable cool environment in office buildings and homes. Similarly, in the case of automobiles, during the summer months, it is well known that the operation of an automobile air conditioner for maintaining cool air within the automobile, places a substantial load on the engine and increases the fuel consumption considerably.
Since electrical power is generated largely by the use of fossil fuels, and since automobiles are almost entirely powered by fossil fuels, it will be appreciated that the amount of fuel expended simply to cool interior environments, during the hot weather, is very considerable. This fuel consumption can sometimes be so great as to impair the air quality of the ambient air, and can, in some cases, actually threaten the stability of the electrical power supply utility itself.
A further and more significant disadvantage of the compression expansion gas cycle heat exchanger is the fact that, as in the case of almost all mechanical devices, it eventually wears out, and the seals entrapping the gas within the closed circuit compression/ expansion loop become worn. As a result, the gas is allowed to escape into the atmosphere. It is now widely believed that the escape of such gases into the upper atmosphere of the earth is responsible for certain changes in the upper atmosphere which are likely to have long term serious and harmful effects for the entire population of the earth.
Another problem which was typically encountered in the actual operation of most air conditioner systems on the normal condition is the fact that they are operating in a relatively humid atmosphere i.e. the air is laden with water vapour. Because the air is at a relatively high temperature, in hotter seasons when air conditioning is required, while the relative humidity of the air at that temperature may not appear to be significantly high or unusual, once it is attempted to reduce the temperature of the air, the relative humidity of the colder air is proportionately increased. As a result, in most typical air conditioning systems, while the operation of the air conditioner may be effective to reduce the temperature of the air by a few degrees, it does not significantly increase the actual comfort level experienced by persons within that air conditioned environment. This is due to the fact that, as the temperature goes down, the humidity goes up, and although the air temperature is slightly less, it does not feel significantly cooler, since the humidity is noticeably higher.
In order to bring the environment down to a more reasonable comfort level it is necessary to both reduce the temperature of the air and to reduce the humidity level. However typically, in the operation of a normal air conditioner, while the air conditioner can quite readily reduce the temperature of the air a few degrees, it then reaches a level at which it must not only reduce the temperature of the air, but it must also cause actual condensation of the water vapour out of the atmosphere. As is well know, when water vapour is condensed it must give up the latent heat of condensation. This latent heat must then be disposed off by the air conditioner before the air conditioner can produce any further significant reduction in the air temperature, and comfort level, within that environment. It is of course possible to provide an air conditioner of excessively high heat transfer capacity, for a given environmental space. This will then produce a rapid dehumidification of the air. However the resultant atmosphere as experienced by persons in that environment, is found to be excessively dry. These factors are of course very well known to air conditioning engineers, and the calculation of the heat transfer capacity of an air conditioner required for a given space is generally speaking a balance or "trade off" between a somewhat under specified system, which will not produce excessive drying, but which will take a significant time to produce a drop in temperature, and an overspecified system which will result in an excessive drying of the atmosphere, but which will reduce the temperature over a shorter space of time. In practice, where it is likely that the air conditioner will be in more or less continuous 24 hour operation within a given environment, at least during hot weather, the general rule is to attempt to slightly underspecify the heat extraction capacity of the air conditioning system. This means that the air conditioner will operate in a more or less "steady state" condition, maintaining an environment at a stable temperature and at a stable humidity level.
There are however certain disadvantages in this practice. When an air conditioner is to be operated under such steady state conditions, it means that the unit will be in operation more or less continuously over a 24 hour duty cycle as long as the weather remains hot. As a result, the unit may have a somewhat shorter of a life span, or alternatively require servicing at more frequent intervals, than would be the case if a unit having a somewhat higher capacity had been specified.
Other forms of heat exchange cycle devices are used in commercial buildings. These usually simply involve water chillers, and a water circulation system whereby chilled water is pumped through the radiators in a commercial building, during the hot season. Heat exchangers and evaporators are usually located, for example, on the roof of a building. These systems while, generally speaking, being less harmful in terms of releasing gases into the atmosphere, still require the consumption of substantial amounts of electrical power in most cases.
Other systems which have been used in the past are the so-called "ammonia" cycle cooling system and also the "lithium-bromide" cooling cycle. Both of these systems also make use of the physical properties of the chemical involved, which goes through a change of state, during the cycle and thus transfers heat from an enclosed space, to some other point where it may be dissipated into the atmosphere. While these systems are somewhat less harmful than the conventional "Freon" (trade mark) cycle systems, they are also known to be somewhat less efficient and thus do not produce the same cooling efficiency, thus requiring still more fuel consumption and are consequently not as popular with consumers.
As a result, notwithstanding all of the well known disadvantages of the typical "Freon" compression expansion heat exchange cycle, the "Freon" gas heat exchanger is by far the most widely used method of heat exchange, in use at the present time.
Clearly, it is desirable to provide a heat exchange system wherein both problems are overcome. Ideally such a heat exchange system should be characterized by a complete absence of any harmful pollutants which can escape from the system and, at the same time, should use as little as possible in the way of energy input required to operate them.
Since, in many situations, heat exchangers are required where there is already an excess of "waste" heat, it is clearly desirable, if possible, that any power requirements required for the operation of such a heat exchanger shall be generated by recycling waste heat. This is particularly true, for example, in the vehicle industry. In this particular case, it is clearly desirable, as far as possible, to provide a heat exchanger which does not draw energy from the prime mover, but instead depends for its energy source on waste heat generated by the prime mover which is otherwise simply vented to atmosphere either through the exhaust system or through the engine coolant system.
In the particular case of the vehicle industry, the designing of a high efficiency heat exchanger, which does not utilize harmful pollutants, is particularly desirable for another reason. In recent years, governments, in various countries, have attempted to discourage the installation of air conditioners in automobiles. Governments have been motivated by various reasons, other than the simple extraction of tax revenues. In the first place, as explained above, such heat exchangers eventually leak and vent harmful pollutants to the atmosphere. In the second place, they cause excess consumption of fossil fuels. These cause undesirable emissions to the atmosphere and, in the case of some countries, use up precious foreign exchange resources, which would better be used for the purchasing of other forms of supplies, unobtainable in those countries.
In some countries, therefore, a special air conditioner tax has been adopted. This tax must be paid when a new vehicle is obtained incorporating air conditioning in its ventilation system.
In some countries automobile air conditioners using the "Freon" cycle system have simply been prohibited altogether, as of a certain future date.
Clearly, therefore, it is desirable from all points of view to provide a different form of air conditioning for vehicles, or for other purposes which does not offend any government regulations and does not involve or incur the payment of additional taxes.
A further factor in the design of such an improved air conditioner is that there exists a very substantial market in the vehicle industry and, in particular, in the commercial side of the vehicle industry, i.e., commercial vehicles and trucks, as well as in private automobiles, for the retrofitting of air conditioners to vehicle ventilation systems. This arises both in the case of older automobiles which have not been built with air conditioners. However, it also applies in the case of newer smaller horsepower vehicles sold at the lower end of the price range, where the air conditioner tax is a significant discouragement to the consumer and, in addition, where the operation of an air conditioner on a relatively lower horsepower vehicle would substantially interfere with its performance.
In the commercial vehicle industry on the other hand, air conditioners are often not specified in the ventilation systems due to the penalty of an increase in fuel consumption. Such commercial vehicles which are operated over many hundreds of thousands of miles a year, must be operated with a predictable rate of fuel consumption. If air conditioners are incorporated in such vehicles, and the fuel consumption increases, then it significantly interferes with the economics of the operation of such a vehicle. As a result, there has been considerable resistance to the installation of air conditioners in such commercial vehicles.
This "after market" for air conditioners which can be retrofitted into existing vehicles is very substantial. However, existing vehicle air conditioners based on the "Freon" cycle of compression and expansion cannot easily be retrofitted and, in addition, even if they are, require the payment of the air conditioner tax in those jurisdictions where it is applicable, and also reduce vehicle performance and increase fuel consumption.
Clearly, therefore, it is desirable that in the design of a new air conditioning cycle that it shall be capable of being retrofitted into vehicle ventilation systems which do not already have air conditioning systems, and that it may have such a design that it does not incur the air conditioning tax or other regulations in certain jurisdictions, and that it does not emit harmful pollutants or use fossil fuels to any extent.
It is also desirable to provide such an air conditioning unit which may be operated efficiently over a relatively wide range of variations in humidity levels of the ambient air within the environment, and which will maintain a substantially stable cool temperature, and a substantially stable relative humidity in such cool environment.